Turndown thermocompressor design for continuous catalyst recovery

ABSTRACT

Systems and processes for regenerating catalyst are provided herein that include a catalyst regeneration tower having a cooling zone that receives a catalyst cooling stream generated by a cooling gas loop. The systems and processes include a first thermocompressor that utilizes a first motive vapor and a second thermocompressor that utilizes a second motive vapor in order to provide the catalyst cooling stream to the regeneration tower. The second thermocompressor operates in parallel with the first thermocompressor. The first thermocompressor can utilize combustion air as the motive vapor. The second thermocompressor can utilize nitrogen as the motive vapor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of copending application Ser. No.12/394,108 filed on Feb. 27, 2009, the contents of which are herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The systems and processes disclosed herein relate to the regeneration ofspent catalyst in the art of catalytic conversion of hydrocarbons touseful hydrocarbon products, and more particularly to thermocompressorsutilized in a continuous catalyst regeneration (CCR) process.

DESCRIPTION OF RELATED ART

The catalysts used in catalytic processes for the conversion ofhydrocarbons tend to become deactivated for one or more reasons. Ininstances where the accumulation of coke deposits causes thedeactivation, regenerating of the catalyst to remove coke deposits canrestore the activity of the catalyst. Coke is normally removed fromcatalyst by contact of the coke-containing catalyst at high temperaturewith an oxygen-containing gas to combust and remove the coke in aregeneration process. These processes can be carried out in-situ, or thecatalyst may be removed from a reactor in which the hydrocarbonconversion takes place and transported to a separate regeneration zonefor coke removal. Various arrangements for continuously orsemicontinuously removing catalyst particles from a reaction zone andfor coke removal in a regeneration zone have been developed.

Some continuous catalyst regeneration systems provide a thermocompressorto facilitate continued operation of the continuous catalystregeneration processes during brief periods of operation under low cokeconditions. One system utilizing a thermocompressor is described, forexample, in PCT Application No. PCT/US2006/062647, the content of whichis hereby incorporated by reference in its entirety. A thermocompressorcan circulate air from the outlet of the air heater to mix withcombustion air going to the cooling zone and provide a net amount ofcombustion air to the cooling zone. The thermocompressor can utilizecombustion air as the motive air, and difficulties in maintainingoperation of the system can occur because the net quantity of combustionair in low coke conditions may be insufficient to satisfy the minimumflow requirement for the air heater and/or for cooling the catalyst.

SUMMARY OF THE INVENTION

The systems and processes disclosed herein relate to continuous catalystregeneration, particularly to such systems and processes that utilize aplurality of thermocompressors to facilitate continuous catalystregeneration under low coke conditions.

In one aspect, a catalyst regeneration system system is provided thatincludes a catalyst regeneration tower, a first thermocompressor, asecond thermocompressor in parallel with the first thermocompressor, andone or more valves. The catalyst regeneration tower includes a coolingzone that receives a catalyst cooling stream. The first thermocompressorutilizes a first motive vapor. The second thermocompressor utilizesnitrogen as a motive vapor. The one or more valves can selectivelydirect a cooled stream to at least one of the first thermocompressor orthe second thermocompressor to produce the catalyst cooling stream.

In a second aspect, a process for providing a catalyst cooling stream toa catalyst regeneration tower is provided that includes selectivelyproviding a cooled stream to at least one of a first thermocompressor ora second thermocompressor, to produce a catalyst cooling stream. and Thefirst thermocompressor utilizes a first motive vapor. The secondthermocompressor utilizes a second motive vapor. The catalyst coolingstream can be provided to a catalyst cooling zone in a catalystregeneration tower.

In a third aspect, a process for regenerating catalyst is provided thatincludes removing a first gas stream from a regeneration tower, passingthe first gas stream to an air heater to form a heated first gas stream,dividing the heated first gas stream to form a regeneration tower returnstream and a cooling loop stream, cooling the cooling loop stream in acooling zone cooler to form a cooled stream, selectively providing thecooled stream to at least one of a first thermocompressor or a secondthermocompressor to produce a catalyst cooling stream, and providing thecatalyst cooling stream to the regeneration tower. The firstthermocompressor utilizes a first motive vapor. The secondthermocompressor utilizes a second motive vapor.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific examples have been chosen for purposes of illustration anddescription, and are shown in the accompanying drawings, forming a partof the specification.

FIG. 1 is a simplified flow diagram of a portion of a continuouscatalyst regeneration process that includes a cooling gas loop.

DETAILED DESCRIPTION

FIG. 1 is a simplified flow diagram of a continuous catalystregeneration (CCR) system indicated generally at 100. As illustrated,spent catalyst 102 can be removed from a reactor and provided to acatalyst regeneration tower 104. The catalyst regeneration tower 104 canhave a plurality of regeneration zones or stages through which the spentcatalyst passes when undergoing regeneration. As illustrated,regeneration tower 104 includes a combustion zone 106, a halogenationzone 108, a drying zone 110, and a cooling zone 112. Spent catalyst canenter the regeneration tower 104 through an inlet at the top of theregeneration tower 104. Upon entering the regeneration tower 104, thespent catalyst can undergo the regeneration process by enteringcombustion zone 106, and then subsequently proceeding through thehalogenation zone 108, the drying zone 110, and the cooling zone 112.Regenerated catalyst 114 can be removed from the catalyst regenerationtower 104, and can be returned to the reactor.

As illustrated in FIG. 1, the continuous catalyst regeneration process100 has a cooling gas loop 116. Cooling gas loop 116 includes a firstgas stream 118 that is removed from a cooling zone outlet 120 in thecooling zone 112 of the regeneration tower 104. First gas stream 118 cancontain air, and can have a temperature of from about 300° F. (149° C.)to about 1000° F. (538° C.). First gas stream 118 can be passed througha conduit to an air heater 122. Air heater 122 heats the first gasstream 118, for example to a temperature of about 1050° F. (566° C.), toform a heated first gas stream 124. The heated first gas stream 124exits the air heater 122, and can be divided into at least two gasstreams, including a regeneration tower return stream 126 and a coolingloop stream 128. The regeneration tower return stream 126 can be passedthrough a conduit back to the regeneration tower 104, and can beprovided to the drying zone 110. After it enters the drying zone, thegas in the regeneration tower return stream 126 can rise within theregeneration tower 104, and can be utilized in the combustion zone 106.

The cooling loop stream 128 can be passed through a conduit to a coolingzone cooler 130. Cooling zone cooler 130 can be a heat exchanger, and ispreferably an indirect heat exchanger such as, for example, a doublepipe heat exchanger, or a shell and tube type heat exchanger. When thecooling zone cooler 130 is a shell and tube exchanger, the cooling loopstream 128 can be passed through the tube side of the cooling zonecooler 130 to form cooled stream 132.

The cooling zone cooler 130 can be cooled with any suitable medium, suchas air or water. For example, as illustrated in FIG. 1, a cooler blower134 can receive atmospheric air, or ambient air from the outdoors, andcan provide an atmospheric air stream 136 to the cooling zone cooler 130to act as a cooling fluid for cooling loop stream 128. When cooling zonecooler is a shell and tube type heat exchanger, for example, atmosphericair stream 136 can be provided to the shell side of the cooling zonecooler 130.

As shown in FIG. 1, cooling gas loop 116 can include one or morethermocompressors, such as a first thermocompressor 138 and a secondthermocompressor 140. Generally, the thermocompressors 138 and 140 canutilize the kinetic energy of a primary fluid, such as the first andsecond motive vapors described below, to pump a secondary fluid, such ascooled stream 132. The first thermocompressor can utilize a first motivevapor, and the second thermocompressor can utilize a second motivevapor. The second motive vapor can preferably have a composition that isdifferent from the composition of the first motive vapor. For example,as illustrated in FIG. 1, first thermocompressor 138 can utilizecombustion air as the first motive vapor, and second thermocompressor140 can utilize nitrogen as the second motive vapor.

First thermocompressor 138 and second thermocompressor 140 arepreferably configured to operate in parallel. The cooled stream 132 canbe selectively directed, and can be provided to at least one of thefirst thermocompressor or the second thermocompressor to produce acatalyst cooling stream 148. The cooled stream 132 can form at leastpart of the catalyst cooling stream 148. Catalyst cooling stream 148 canalso include the motive vapor of any thermocompressor to which thecooled stream 132 is provided. Catalyst cooling stream 148 can thusinclude the first motive vapor, the second motive vapor, or both thefirst and second motive vapors. Catalyst cooling stream 148 can bepassed through a conduit to an inlet 150 of the regeneration tower 104,and can be provided to the cooling zone 112 of the catalyst regenerationtower 104.

The cooled stream 132 can be provided to the first thermocompressor 138,to the second thermocompressor 140, or can be divided and provided toboth the first thermocompressor 138 and the second thermocompressor 140.One or more valves, such as illustrated valve 154, can be utilized toselectively direct the cooled stream 132. The one or more valves can beoperated by one or more switches, such as, for example, a softwareswitch. The cooled stream 132 can be selectively directed based uponoperating conditions, including, but not limited to, catalyst cokelevel, instrument header pressure, and other operating conditions.

In some instances, it may be desirable to operate the firstthermocompressor 138 during a first set of operating conditions, and tooperate the second thermocompressor 140 during a second set of operatingconditions. For example, the cooling gas loop 116 can utilize firstthermocompressor 138 under normal operating conditions, or for shortterm operations under low coke conditions, and can utilize secondthermocompressor 140 for operation during periods of continuous low cokeconditions.

With respect to the utilization of the first thermocompressor 138, thefirst motive vapor 142 can be supplied to the first thermocompressor 138through dryer 144. As shown in FIG. 1, dryer 144 can receive a gasstream 146, and can supply motive vapor 142 through a conduit to thefirst thermocompressor 138. The gas stream 146 can be air, and caninclude oxygen and nitrogen. The flow rate or amount of the first motivevapor 142 can be controlled based upon the amount of oxygen required bythe combustion zone 106. The flow rate for the first motive vapor 142can be based on a reduced combustion air rate, such as, for example,about 25% of the design combustion air, and a reduced instrument airheader pressure, such as, for example, a pressure that is about 10 psilower than the pressure available under normal operating conditions.

To facilitate the operation of the first thermocompressor 138 undercertain conditions, such as, for example, longer term low coke or verylow coke operation conditions, a nitrogen stream 152 can be provided andcombined with the first motive vapor 142 to add motive flow for thefirst thermocompressor 138. The nitrogen stream 152 can provide addedmotive gas flow and gas pressure to help satisfy the processrequirements, the nitrogen results in reduced oxygen concentration inthe chlorination zone of the regeneration tower. Over extended periodsof time, however, the lower oxygen concentration in the chlorinationzone of the regeneration tower may adversely impact the quality of thecatalyst regeneration.

With respect to utilization of the second thermocompressor 140, nitrogenstream 152 can be received by the second thermocompressor 140, and canact as the second motive vapor for the second thermocompressor 140.Nitrogen stream 152 can consist substantially completely of nitrogen.The nitrogen stream 152 can be provided to the second thermocompressor140 at a higher pressure than the combustion air utilized as the motivevapor for first thermocompressor 138. The second thermocompressor 140can thus operate at a higher ratio of load gas to motive gas than thefirst thermocompressor 138. The higher ratio can provide additional loadgas flow to maintain long term low coke operation while maintaining anappropriate oxygen concentration in the halogenation zone 108 of theregeneration tower 104. In some examples, the pressure of nitrogenstream 152 can be from about 30 psi to about 300 psi higher than thepressure of the combustion air utilized as the motive vapor for thefirst thermocompressor 138. The flow rate of nitrogen stream 152 canpreferably be controlled to maintain the oxygen content in thehalogenation zone 108 at a level of above about 10%, and preferably at alevel of above about 18%.

From the foregoing, it will be appreciated that although specificexamples have been described herein for purposes of illustration,various modifications may be made without deviating from the spirit orscope of this disclosure. It is therefore intended that the foregoingdetailed description be regarded as illustrative rather than limiting,and that it be understood that it is the following claims, including allequivalents, that are intended to particularly point out and distinctlyclaim the claimed subject matter.

1. A catalyst regeneration system, the system comprising: a catalystregeneration tower including a cooling zone that receives a catalystcooling stream; a first thermocompressor that utilizes a first motivevapor; and a second thermocompressor in parallel with the firstthermocompressor that utilizes nitrogen as a motive vapor; and one ormore valves that selectively direct a cooled stream to at least one ofthe first thermocompressor or the second thermocompressor to produce thecatalyst cooling stream.
 2. The catalyst regeneration system of claim 1,further comprising: an air heater that receives a first gas streamremoved from the regeneration tower and produces a heated first gasstream; and a cooling zone cooler that receives at least a portion ofthe heated first gas stream and produces the cooled stream.
 3. Thecatalyst regeneration system of claim 2, wherein the catalystregeneration tower includes a combustion zone, a halogenation zone, adrying zone, and a cooling zone.
 4. The catalyst regeneration system ofclaim 3, wherein the first gas stream is removed from the cooling zone112 of the regeneration tower.
 5. The catalyst regeneration system ofclaim 1, wherein the first motive vapor is supplied to the firstthermocompressor through a dryer.
 6. The catalyst regeneration system ofclaim 5, wherein the first motive vapor contains oxygen and nitrogen. 7.The catalyst regeneration system of claim 1, wherein the nitrogen isprovided to the second thermocompressor at a higher pressure than thefirst motive vapor is provided to the first thermocompressor.
 8. Thecatalyst regeneration system of claim 7, wherein the pressure of thenitrogen is about 30 psi to about 300 psi higher than the pressure ofthe first motive vapor.
 9. The catalyst regeneration system of claim 1,wherein the second thermocompressor operates at a higher ratio of loadgas to motive gas than the first thermocompressor.
 10. The catalystregeneration system of claim 1, wherein the nitrogen has a flow ratethat is controlled to maintain the oxygen content in the halogenationzone at a level of above about 18%.